JP7481738B2 - Platinum-supported molybdenum oxide catalyst and method for producing carbon monoxide and methanol using said catalyst - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act. Presented at the 62nd Annual Meeting of the Japan Petroleum Institute held at Tower Hall Funabori on May 29, 2019.

Application of Article 30, Paragraph 2 of the Patent Act Presented at the 124th Catalyst Symposium of the Catalysis Society of Japan held at Nagasaki University on September 18, 2019

The present invention relates to a platinum-supported molybdenum oxide catalyst and a method for producing carbon monoxide and methanol by reducing carbon dioxide in the presence of the catalyst.

Global warming caused by the large amount of carbon dioxide (CO ₂ ) emitted from the consumption of fossil fuels such as coal and oil is becoming more serious year by year. Therefore, research into the control and reduction of carbon dioxide emissions is being actively promoted on a global scale in order to solve global warming. For example, if carbon dioxide can be used as a carbon source and converted into carbon monoxide (CO) or methanol (CH ₂ OH) using catalytic technology, it will be possible to chemically fix carbon dioxide, which is a cause of global warming, as a basic chemical product.

Carbon monoxide and methanol are generally produced by the following methods. For example, carbon monoxide is obtained by refining and separating the synthesis gas obtained by the steam reforming reaction shown in formula (1) below using methane contained in natural gas (LNG) and liquefied petroleum gas (LPG), i.e., fossil fuel, as the raw material. The steam reforming reaction is carried out under high pressure and at a high temperature of 600°C or higher using a nickel (Ni)-based catalyst.

_CH4 + _H2O → CO + _3H2 ; _ΔH2980 = 206 ^kJ /mol (1)

Another method for producing carbon monoxide is the reverse water gas shift reaction shown in formula (2) below. Because this is an endothermic reaction, a high temperature of 400°C or higher is generally required.

CO ₂ + H ₂ → CO + H ₂ O; ΔH ₂₉₈ ⁰ = 41.2 kJ / mol (2)

On the other hand, methanol is generally produced by reacting CO, which is generated in the steam reforming reaction shown in the above formula (1), with _H2 at high temperature (240 to 300°C) and high pressure (50 to 100 atm).

As such, typical methods for producing carbon monoxide and methanol use many fossil fuels as raw materials, and require high temperature and pressure conditions. For this reason, in recent years, various research projects have been conducted with the aim of converting carbon dioxide into carbon monoxide and methanol under milder conditions. In addition, the use of carbon dioxide present in the atmosphere and carbon dioxide emitted in large quantities from power plants as raw materials is being considered.

For example, methods for synthesizing carbon monoxide under visible light irradiation have been reported, such as a method using palladium-supported hydrogen-doped tungsten oxide (Pd/H _y WO _3-x ) as a catalyst (Non-Patent Document 1) and a method using a catalyst in which a part of the surface of Pd/H _y WO _3-x is modified with copper (Cu) (Non-Patent Document 2).

In addition, a method for synthesizing methanol from a mixed gas of carbon dioxide and hydrogen using a catalyst (Pt/ _MoOx / _TiO2 ) in which platinum (Pt) and molybdenum oxide ( _MoOx ) are supported on titanium dioxide ( _TiO2 ) (Non-Patent Document 3), and a method for synthesizing methanol from a mixed gas of carbon dioxide and hydrogen using a copper/zinc oxide (Cu/ZnO) catalyst with various elements added thereto (Patent Document 1) have been reported.

On the other hand, Non-Patent Document 4 and Patent Document 2 report a method for synthesizing sulfide by deoxygenation of sulfoxide under visible light irradiation using platinum-supported molybdenum trioxide (Pt/MoO ₃ ) as a catalyst.

Incidentally, when Pt/MoO ₃ is subjected to hydrogen reduction treatment at high temperature, surface plasmon resonance occurs and the material exhibits light absorption from the ultraviolet to infrared regions (Non-Patent Document 5).

JP 2014-057925 A JP 2018-076261 A

Li et al., ACS Appl. Mater. Interfaces, 2019, 11, 5610-5615 Li et al., J. Am. Chem. Soc., 2019, 141, 14991-14996 Toyao et al., ACS Catal., 2019, 9, 8187-8196 Kuwahara et al., J. Am. Chem. Soc., 2018, 140, 9203-9210 Cheng et al., J. Am. Chem. Soc., 2016, 138, 9316-9324

As described above, the production of carbon monoxide or methanol by the reduction reaction of carbon dioxide has been investigated, but no highly active catalyst that can efficiently carry out the reduction reaction of carbon dioxide under sufficiently mild conditions has been reported so far.

One aspect of the present invention relates to a platinum-supported Mo oxide catalyst that comprises a Mo oxide containing molybdenum trioxide and platinum particles supported on the Mo oxide, and promotes a reaction that produces at least one of carbon monoxide and methanol by reduction of carbon dioxide.

Another aspect of the present invention relates to a method for producing carbon monoxide/methanol, comprising a step of carrying out a deoxygenation reaction of carbon dioxide in the presence of the platinum-supported Mo oxide catalyst and hydrogen to produce at least one of carbon monoxide and methanol.

According to the present invention, carbon dioxide can be efficiently reduced under mild conditions to produce carbon monoxide. Also, according to the present invention, carbon dioxide can be efficiently reduced under mild conditions to produce methanol.

1 is an ultraviolet-visible-near infrared (UV-Vis-NIR) absorption spectrum of a platinum-supported Mo oxide catalyst. This is a signal obtained by temperature programmed reduction (H ₂ -TPR) of a platinum-supported oxide catalyst. 1 is an X-ray diffraction (XRD) spectrum of a platinum-supported Mo oxide catalyst. 1 is an X-ray photoelectron spectroscopy (XPS) spectrum of a platinum-supported Mo oxide catalyst. 1 is a transmission electron microscope (TEM) photograph of a platinum-supported Mo oxide catalyst. FIG. 2 is a graph showing the change over time in the amount of product produced in the deoxygenation reaction of carbon dioxide. FIG. 2 is a graph showing the change over time in product selectivity in the deoxygenation reaction of carbon dioxide. FIG. 1 is a graph showing the relationship between the hydrogen reduction treatment temperature of a platinum-supported Mo oxide catalyst and the carbon dioxide conversion rate and product selectivity. FIG. 1 is a graph showing the relationship between the hydrogen reduction treatment temperature of a platinum-supported Mo oxide catalyst, the amount of hydrogen doping (x), the amount of oxygen vacancies (y), and the product yield. FIG. 1 is a diagram showing the difference in activity of a platinum-supported Mo oxide catalyst under visible light irradiation and in the dark. FIG. 1 shows the results of a carbon dioxide deoxygenation reaction using a metal-supported Mo oxide catalyst under visible light irradiation. FIG. 1 shows the results of a carbon dioxide deoxygenation reaction using a platinum-supported oxide catalyst under visible light irradiation. FIG. 1 is a diagram showing the difference in catalytic activity of a platinum-supported Mo oxide catalyst under visible light irradiation depending on the hydrogen reduction treatment temperature. FIG. 1 is a graph showing the relationship between the hydrogen reduction treatment temperature of a platinum-supported Mo oxide catalyst and the amount of hydrogen doping (x), the amount of oxygen vacancies (y), and the amount of carbon monoxide produced under visible light irradiation. FIG. 1 shows the results of a carbon dioxide deoxygenation reaction under light irradiation by a light-emitting diode (LED). FIG. 1 shows a comparison of the UV-Vis-NIR absorption spectrum of a platinum-supported Mo oxide catalyst with the wavelength of an LED.

[Platinum-supported Mo oxide catalyst]
The platinum-supported Mo oxide catalyst according to the embodiment of the present invention comprises Mo oxide containing molybdenum trioxide (MoO ₃ ) and platinum (Pt) particles supported on the Mo oxide. The platinum-supported Mo oxide catalyst promotes a reaction of producing at least one of carbon monoxide and methanol by reduction of carbon dioxide. In the presence of hydrogen, methanol is produced at a high yield by the deoxygenation reaction of carbon dioxide.

MoO ₃ in the platinum-supported Mo oxide catalyst may have oxygen defects. The oxygen defects can be active sites for the deoxidation reaction of carbon dioxide. The oxygen defects are generated when molybdenum trioxide (Pt/MoO ₃ ) carrying Pt particles is subjected to hydrogen reduction treatment under appropriate conditions. Hydrogen atoms cleaved on the Pt particles and adsorbed on Pt spill over into MoO ₃ , and H ₂ O generated by bonding with oxygen atoms in MoO ₃ is released. At this time, the oxygen defects formed in MoO ₃ and the hydrogen atoms and electrons introduced into MoO ₃ are controlled by the reduction treatment conditions to obtain a more active platinum-supported Mo oxide catalyst.

The introduction of oxygen defects into _MoO3 of the platinum-supported Mo oxide catalyst can be confirmed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, etc. When the platinum-supported Mo oxide catalyst is subjected to hydrogen reduction treatment at around room temperature, it shows a structure close to the orthorhombic crystal of _MoO3 . As the reduction temperature increases, it takes on an amorphous structure represented by the general formula: _{HxMoO3 -y} . When the reduction temperature is 300°C or higher, it takes on a structure close to the monoclinic crystal of molybdenum dioxide ( _MoO2 ). That is, the Mo oxide contained in the platinum-supported Mo oxide catalyst contains _MoO2 , _{HxMoO3 -y,} etc. in addition to _MoO3 , depending on the conditions of the hydrogen reduction treatment.

Pt has a higher ability to split hydrogen than metals such as copper (Cu) and nickel (Ni). Therefore, Pt can split hydrogen even by hydrogen reduction treatment at relatively low temperatures from around room temperature to about 200 °C, making it possible to introduce oxygen vacancies into _MoO3 .

When carbon dioxide deoxygenation is carried out in the presence of a platinum-supported Mo oxide catalyst and hydrogen, the Mo oxide is preferably represented by _{HxMoO3 -y} and has an amorphous structure. By using such a catalyst, the conversion rate of carbon dioxide and the selectivity to the produced carbon monoxide and methanol are increased.

When Mo oxide is represented by _{HxMoO3 -y} , x represents the amount of hydrogen doped that is cleaved by Pt particles and adsorbed or absorbed by Mo oxide. Also, y represents the amount of oxygen vacancies introduced. Here, the amount of hydrogen doped (x) and the amount of oxygen vacancies (y) are values obtained by thermogravimetry (TG). Based on the values measured for the mass change of the platinum-supported Mo oxide catalyst when the temperature is changed in air and nitrogen gas, the values of x and y can be obtained from the following formulas (3) and (4).

(Measured in air)
_{HxMoO3 -y} + O2 _(air) → _MoO3 + 1/ _2xH2O (3)

(Measured in nitrogen)
_{HxMoO3 -y} → MoO3 _-y-x/2 + 1/ _2xH2O (4)

As the hydrogen reduction temperature increases, the hydrogen doping amount (x) decreases and the amount of oxygen defects (y) increases. In order to introduce an appropriate amount of oxygen defects into the platinum-supported Mo oxide catalyst and increase the yield of carbon monoxide and methanol produced in the carbon dioxide deoxygenation reaction, it is preferable that the hydrogen doping amount (x) and the amount of oxygen defects (y) satisfy the conditions 0<x<2.0 and 0.1≦y<1. It is more preferable that y is 0.1 or more and 0.9 or less. In particular, since the catalytic activity becomes high, it is even more preferable that y is 0.2 or more and 0.8 or less.

To obtain a preferred amount of hydrogen doping (x) and oxygen vacancies (y), the mass of the Pt particles supported on the Mo oxide is preferably 0.1% or more and 5% or less of the mass of the Mo oxide, and more preferably 1% or more and 4% or less.

The Pt particles of the platinum-supported Mo oxide catalyst may contain a metal element M1 other than Pt. That is, the platinum particles may be alloy particles whose main component is platinum. The main component refers to a component that is more than 50 mass% of the alloy. Examples of M1 include copper (Cu), nickel (Ni), cobalt (Co), gold (Au), ruthenium (Ru), palladium (Pd), silver (Ag), and indium (In). Among these, Cu is preferred because it maintains high catalytic activity equal to or higher than that when the Pt particles are made of only Pt. M1 may be used alone or in combination of two or more types.

The Mo oxide serving as the carrier may also contain a metal element M2 other than Mo. Examples of M2 include tungsten (W), rubidium (Rb), cerium (Ce), cesium (Cs), vanadium (V), rhenium (Re), chromium (Cr), and tantalum (Ta). Among these, W, V, and Cr are preferred because they maintain catalytic activity equal to or higher than that of a Mo oxide containing only Mo as a metal element. M2 may be used alone or in combination of two or more types.

It is preferable that the platinum-supported Mo oxide catalyst does not contain titanium oxide. Titanium oxide can reduce the activity of the platinum-supported Mo oxide catalyst in the reduction reaction of carbon dioxide (i.e., the production reaction of carbon monoxide and/or methanol).

[Surface Plasmon Resonance]
When oxygen defects are introduced into MoO ₃ , the electron density in the oxide increases, and surface plasmon resonance may occur with a change in the band structure. The occurrence of surface plasmon resonance can be confirmed, for example, by ultraviolet-visible-near infrared (UV-Vis-NIR) absorption spectroscopy. A platinum-supported Mo oxide catalyst in which oxygen defects have been introduced by hydrogen reduction treatment at temperatures from around room temperature to 300 ° C. may exhibit light absorption from the ultraviolet region to the infrared region, and may exhibit strong light absorption due to surface plasmon resonance, particularly from 500 nm to 600 nm. This means that surface plasmon resonance of the Mo oxide in the platinum-supported Mo oxide catalyst is induced under irradiation of visible light. When hydrogen reduction treatment is performed at a high temperature exceeding 300 ° C, the platinum-supported Mo oxide catalyst takes a structure close to the monoclinic crystal of MoO ₂ , making it difficult to exhibit surface plasmon resonance. Therefore, the platinum-supported Mo oxide catalyst is particularly highly active in a state where surface plasmon resonance can be exhibited.

When the platinum-supported Mo oxide catalyst contains a carrier other than Mo oxide, such as titanium oxide, the Mo oxide may be highly dispersed on the titanium oxide, making it difficult to exhibit surface plasmon resonance. Therefore, it is preferable that the platinum-supported Mo oxide catalyst does not contain titanium oxide or the like.

[Carbon dioxide deoxygenation reaction]
The reaction in which at least one of carbon monoxide and methanol is produced by the deoxidation reaction of carbon dioxide in the presence of a platinum-supported Mo oxide catalyst is believed to be due to the following mechanism. When carbon dioxide is brought into contact with a platinum-supported Mo oxide catalyst, one of the oxygen atoms of carbon dioxide is adsorbed and coordinated to the oxygen vacancies of MoO _3. This causes a deoxidation reaction of carbon dioxide to produce carbon monoxide. Under conditions of high partial pressure of carbon dioxide, carbon monoxide further moves onto the Pt particles, and the hydrogen atoms produced by cleavage on the Pt particles are successively added to the carbon monoxide to produce methanol. That is, methanol is produced using carbon monoxide as an intermediate. In addition, when hydrogen in the reaction system is cleaved on the Pt particles of the platinum-supported Mo oxide catalyst that has lost the oxygen vacancies, the produced hydrogen atoms spill over into MoO ₃ , producing oxygen atoms in MoO ₃ and H ₂ O, which are then released. This reaction introduces oxygen vacancies into MoO ₃ again, and the high activity of the platinum-supported Mo oxide catalyst is reproduced.

The following provides a more detailed explanation of the platinum-supported Mo oxide catalyst and carbon monoxide/methanol production method according to an embodiment of the present invention.

[Preparation of platinum-supported Mo oxide catalyst]
The platinum-supported Mo oxide catalyst is obtained by fixing Pt particles on the surface of _MoO3 , which serves as a carrier.
The method for preparing _MoO3 is not particularly limited, and for example, it can be prepared by calcining hexaammonium heptamolybdate (AHM) in an air atmosphere and then pulverizing it. The calcination conditions are not particularly limited, but in order to perform the calcination sufficiently, it is preferable to set the calcination temperature to 400°C to 600°C and the calcination time to 1 hour or more.

The method for immobilizing Pt particles on the surface of _MoO3 is not particularly limited. For example, _MoO3 can be dispersed in water, an aqueous solution in which a platinum precursor is dissolved and a reducing agent are added, and then the mixture is stirred to immobilize the Pt particles. The mixture is then filtered or centrifuged, washed with water, and vacuum dried to obtain a platinum-supported Mo oxide catalyst.

The mass of the Pt particles is preferably 0.1% or more and 5% or less, more preferably 1% or more and 4% or less, of the mass of the Mo oxide. At this time, Pt/MoO ₃ shows high catalytic activity. The average particle diameter of the Pt particles is preferably 1 nm to 10 nm. The average particle diameter of the Pt particles can be obtained, for example, by observing 10 Pt particles with a transmission electron microscope (TEM) and averaging the maximum diameters. By setting the average particle diameter within the above range, hydrogen atoms cleaved on the Pt particle surface are more likely to spill over to the carrier MoO ₃ , improving the catalytic activity. In addition, the decrease in the reaction area due to the aggregation of Pt particles is also suppressed.

From the viewpoint of reaction efficiency, it is preferable that the amount of _MoO3 dispersed in water is 1 g to 50 g per 1000 g of water. _{The MoO3} particles are easily dispersed in water, and the Pt particles are less likely to aggregate.

Examples of platinum precursors that can be used include platinum chloride (II) (PtCl ₂ ), platinum chloride (IV) (PtCl _{4.5H 2} O), chloroplatinic (IV) acid hexahydrate (H ₂ PtCl _{6.6H 2} O), potassium tetrachloroplatinate (II) (K ₂ PtCl ₄ ), potassium hexachloroplatinate (IV) (K ₂ PtCl ₆ ), sodium tetrachloroplatinate (II) (Na ₂ PtCl ₄ ), sodium hexachloroplatinate (IV) (Na ₂ PtCl ₆ ), ammonium tetrachloroplatinate (II) ((NH ₄ ) ₂ PtCl ₄ ), ammonium hexachloroplatinate (IV) ((NH ₄ ) ₂ PtCl ₆ ), bis(acetylacetonato)platinum (II), tetraammineplatinum (II) nitrate, and tetraammineplatinum (II) chloride. Among these, potassium tetrachloroplatinate(II), sodium tetrachloroplatinate(II) and ammonium tetrachloroplatinate(II) are preferred in that they suppress the dissolution of _MoO3 in the platinum precursor aqueous solution.

The concentration of the platinum precursor in the aqueous solution can be appropriately set based on the amount of dispersed MoO _3. In order to further reduce the particle size of the Pt particles fixed on the surface of MoO ₃ , the concentration of the platinum precursor is preferably 0.1 mmol/L to 100 mmol/L. In order to fix a sufficient amount of Pt particles on the surface of MoO ₃ , the amount of the platinum precursor per 1 g of MoO ₃ is 5 μmol to 250 μmol, more preferably 100 μmol to 200 μmol.

The reducing agent has the function of reducing Pt ions contained in the platinum precursor aqueous solution and immobilizing Pt particles on MoO _3. Examples of such reducing agents include chemical reducing agents such as urea, ammonia, sodium borohydride (NaBH ₄ ), potassium borohydride (KBH ₄ ), ammonia borane (NH ₃ BH ₃ ), hydrazine (N ₂ H ₄ ), sodium formate (HCOONa), and ascorbic acid (C ₆ H ₈ O ₆ ). Among them, urea is preferred because it can make the Pt particles immobilized on MoO ₃ smaller. The amount of the reducing agent is not particularly limited and can be appropriately determined depending on the amount of dispersion of MoO ₃ , the concentration of the platinum precursor aqueous solution, the type of reducing agent used, etc., but it is sufficient that it is 1 mol to 100 mol per 1 mol of platinum.

The temperature during stirring after adding the aqueous solution of the platinum precursor and the reducing agent is not particularly limited, but is preferably room temperature to 100°C, and more preferably 60°C to 100°C from the viewpoint of reaction efficiency. The stirring time may be set according to the temperature during stirring, but is preferably 5 minutes to 600 minutes.

When the platinum-supported Mo oxide catalyst contains a metal element M1 other than Pt in the Pt particles, that is, when the Pt particles are alloy particles mainly composed of an alloy, for example, the catalyst is prepared by first fixing the metal element M1 on the surface of MoO ₃ , and then fixing the Pt particles. The fixation of the metal element M1 is carried out, for example, in the same manner as the fixation of the Pt particles, by dispersing MoO ₃ in water, adding an aqueous solution in which the precursor of the metal element M1 is dissolved and a reducing agent, and then stirring. The product (M1/MoO ₃ ) obtained by filtering, washing with water, and vacuum drying may then be fixed with Pt particles. This results in, for example, Pt ₆ Cu/MoO ₃ , which supports alloy particles of Pt and Cu. When two or more kinds of metal elements M1 are contained, the fixation of the metal element M1 using the precursor of the metal element M1 may be repeated two or more times.

As the precursor of the metal element M1, various salts of the metal element M1 (e.g., chloride, chloride oxide, chloride hydroxide, bromide, bromide oxide, iodide, iodide oxide, nitrate, sulfate, etc.), carbonyl compounds, oxides, etc. may be used.
The content of the metal element M1 in the alloy is preferably 50 mol % or less in order to obtain a high catalytic activity equal to or higher than that in the case where only Pt is supported as the metal.

In addition, when the Mo oxide that is the carrier of the platinum-supported Mo oxide catalyst contains a metal element M2 other than Mo, an oxide containing Mo and a metal element M2 is first prepared, and then Pt particles are fixed on the surface of the obtained oxide. The oxide containing Mo and a metal element M2 can be prepared, for example, by mixing a precursor of Mo and a precursor of a metal element M2 in the same manner as the preparation method of _MoO3 , firing the mixture under an air atmosphere, and then pulverizing the mixture. Then, the obtained oxide (for example, represented by the general formula: M2 _0.05 Mo _{0.95 Oz} ) is dispersed in water, and the Pt particles are fixed in the same manner as described above. This results in, for example, Pt/W _0.05 Mo _{0.95 Oz,} Pt/V _0.05 Mo _{0.95 Oz} , Pt/Cr _0.05 Mo _{0.95 Oz} , etc. being obtained. In the case where two or more kinds of metal elements M2 are contained, similarly, when preparing the oxide, precursors of two or more kinds of metal elements M2 may be mixed with a precursor of Mo and then fired.

Hexaammonium heptamolybdate (AHM) is used as a precursor of Mo. In addition, various salts of the metal element M2 (e.g., chlorides, chloride oxides, chloride hydroxides, bromides, bromide oxides, iodides, iodide oxides, nitrates, sulfates, ammonium salts, etc.), carbonyl compounds, oxides, etc. are used as precursors of the metal element M2.
In order to obtain a catalytic activity equal to or higher than that in the case where only Mo is contained in the support, the content of the metal element M2 in the oxide is preferably 50 mol % or less of the total of Mo and the metal element M2, and more preferably 20 mol % or less.

[Hydrogen reduction treatment of platinum-supported Mo oxide catalyst]
The fact that _MoO3 in Pt/ _MoO3 can be reduced by hydrogen can be confirmed, for example, by temperature programmed reduction ( _H2 -TPR) etc. That is, when a platinum-supported Mo oxide catalyst is subjected to hydrogen reduction treatment, oxygen defects are introduced into _MoO3 .

The hydrogen reduction process is carried out, for example, under a hydrogen partial pressure of 10 kPa to 101.3 kPa. Hydrogen gas may be circulated alone in the reducing atmosphere, or may be mixed with an inert gas (such as nitrogen, helium, or argon gas) in any ratio and circulated.

The hydrogen reduction treatment temperature is preferably in the range of room temperature to 300°C. A platinum-supported Mo oxide catalyst treated at a temperature in this range exhibits high catalytic activity when used as a catalyst for carbon dioxide decomposition. In other words, the conversion rate of the raw material carbon dioxide, and the selectivity and yield of the carbon monoxide and methanol produced are increased. In addition, a platinum-supported Mo oxide catalyst that has been hydrogen-reduced in the above range can exhibit surface plasmon resonance under irradiation with visible light. In particular, the hydrogen reduction treatment temperature is preferably in the range of 200°C to 300°C. The hydrogen reduction treatment time is appropriately determined depending on the treatment temperature, but is preferably 0.5 hours to 48 hours, and particularly preferably 0.5 hours to 2 hours.

[Carbon dioxide deoxygenation reaction]
In the carbon monoxide/methanol production method according to the embodiment of the present invention, a deoxygenation reaction of carbon dioxide is carried out in the presence of a platinum-supported Mo oxide catalyst and hydrogen.

The carbon dioxide deoxidation reaction is carried out, for example, by placing a platinum-supported Mo oxide catalyst in a reaction vessel and introducing carbon dioxide gas and hydrogen gas. The reaction may be carried out in either the gas phase or liquid phase. There are no particular limitations on the reaction vessel, but for example, a closed glass cell is used for the gas phase reaction. Furthermore, when the reaction is carried out under a pressure higher than the standard atmospheric pressure, or for the liquid phase reaction, for example, a closed stainless steel pressure-resistant reaction vessel is used.

When the reaction is carried out in the liquid phase, the following solvents are used: 1,4-dioxane; tetrahydrofuran; dimethyl ether; N,N-dimethylformamide; acetonitrile; chain hydrocarbons such as n-hexane and n-octane; cyclic hydrocarbons such as cyclohexane and cyclooctane; aromatic hydrocarbons such as benzene and p-xylene; saturated alcohols such as ethanol and n-butanol; water, etc. The amount of platinum-supported Mo oxide catalyst and solvent used is determined appropriately depending on the type of platinum-supported Mo oxide catalyst and solvent, the volume of the reaction vessel, the reaction conditions, etc. From the viewpoint of the dispersibility of the catalyst in the solvent, the amount of solvent used is preferably 10 mL to 200 mL per 100 mg of catalyst, and particularly preferably 20 mL to 50 mL.

Before introducing carbon dioxide gas and hydrogen gas into the reaction vessel, the platinum-supported Mo oxide catalyst may be pre-reduced. The pre-reducing process is carried out, for example, by sealing the platinum-supported Mo oxide catalyst in a reaction vessel and heating it under hydrogen gas flow. The pre-reducing process is carried out, for example, under a hydrogen partial pressure of 1 kPa to 2 MPa, but is preferably carried out under a hydrogen partial pressure of normal pressure or lower. Hydrogen gas may be circulated alone in the reducing atmosphere, or may be mixed with an inert gas (nitrogen, helium, argon gas, etc.) at any ratio and then circulated. The amount of hydrogen to be circulated can be appropriately determined depending on the amount of the platinum-supported Mo oxide catalyst, the hydrogen partial pressure, the volume of the reactor used, etc., but when pre-reducing 1 g of the platinum-supported Mo oxide catalyst, it is preferably 10 mL/min to 1000 mL/min. The pre-reducing process temperature may be equal to or lower than the hydrogen reduction process temperature for the purpose of introducing oxygen defects, and is preferably in the range of room temperature to 300°C. The pre-reducing process time is appropriately determined depending on the process temperature, but is preferably 0.5 hours to 2 hours.

There are no particular limitations on the method of introducing carbon dioxide gas and hydrogen gas in the carbon dioxide deoxygenation reaction. For example, in a gas phase reaction, carbon dioxide gas and hydrogen gas may be introduced into the reaction vessel at any pressure. When the reaction is carried out under pressure or in a liquid phase reaction, the reaction may be carried out by sealing or circulating carbon dioxide gas and hydrogen gas in the reaction vessel. There are no particular limitations on the method of sealing or circulating, and the gas may be sealed at any pressure.

In the process of producing carbon monoxide and methanol, which one is more selectively produced depends on the reaction conditions, reaction time, etc. For example, under pressurized conditions, carbon monoxide once produced changes into methanol over time. However, in general, when the total of the partial pressure of carbon dioxide and the partial pressure of hydrogen is, for example, 0.1 MPa or more and 2.0 MPa or less, preferably 0.1 MPa or more and 1.0 MPa or less, carbon monoxide is selectively produced. Under higher pressure conditions of 0.5 MPa or more and 200 MPa or less, preferably 1.0 MPa or more and 200 MPa or less, the selectivity of methanol is high.
When it is desired to selectively produce carbon monoxide, the partial pressure of carbon dioxide is preferably 0.1 MPa or more and 2.0 MPa or less, more preferably 0.1 MPa or more and 1.0 MPa or less. When it is desired to increase the selectivity of methanol, the partial pressure of carbon dioxide is preferably 0.5 MPa or more and 200 MPa or less, more preferably 1.0 MPa or more and 200 MPa or less.

In the carbon monoxide/methanol production method according to the embodiment of the present invention, it is preferable to carry out the carbon dioxide deoxygenation reaction in an atmosphere of 300°C or less. More preferably, it is 250°C or less. From the viewpoint of promoting the reaction, it is preferable to carry out the carbon dioxide deoxygenation reaction at 150°C or more, and more preferably at 200°C or more. In the above temperature range, even if a platinum-supported Mo oxide catalyst having oxygen vacancies loses oxygen vacancies due to the deoxygenation reaction, it can be reduced again by hydrogen present in the reaction system and become a highly active catalyst having oxygen vacancies.

The reaction time can be adjusted as appropriate depending on the reaction temperature, type of catalyst, etc., but it is preferable to set it to 1 to 48 hours.

After the reaction is complete, the products can be separated using, for example, a gas separation membrane. Analysis of the products of the deoxygenation reaction is performed, for example, by using a gas chromatograph-flame ionization detector (GC-FID) with a methanizer for the gaseous products. Liquid products are similarly analyzed by a GC-FID with a methanizer after adding an external standard reagent (for example, 1-butanol) to the reaction solution.

The platinum-supported Mo oxide catalyst used in the carbon dioxide deoxygenation reaction is recovered from the reaction solution by filtration or centrifugation. The recovered catalyst can be reused after washing and drying. By reducing it again through the hydrogen reduction treatment described above, it will once again exhibit high activity similar to that of an unused catalyst.

[Reaction under visible light irradiation]
When oxygen vacancies are introduced into _MoO3 , the platinum-supported Mo oxide catalyst may exhibit light absorption in the ultraviolet to infrared regions, and may exhibit strong light absorption due to surface plasmon resonance, particularly in the range of 500 nm to 600 nm. In such cases, it is possible to efficiently perform the deoxygenation reaction of carbon dioxide under milder conditions under light irradiation.

The deoxygenation reaction of carbon dioxide under light irradiation is carried out in a translucent reaction vessel while irradiating light using a light source such as a xenon lamp, a mercury lamp, or a light-emitting diode (LED) lamp. The irradiated light may be any of ultraviolet light, visible light, and infrared light, and the wavelength may be, for example, 200 nm to 2000 nm. A wavelength of 400 nm to 1000 nm is preferable. In particular, it is preferable to carry out the deoxygenation reaction under irradiation with visible light that induces surface plasmon resonance of Mo oxide. The wavelength of the light can be adjusted by using an appropriate short-wavelength cut filter and a long-wavelength cut filter.

In the carbon dioxide deoxygenation reaction under light irradiation, the catalytic activity of the platinum-supported Mo oxide catalyst is higher than in the reaction in the dark, so the reaction proceeds even at low temperatures, for example, at 150°C or lower. In addition, the higher catalytic activity makes it possible to shorten the reaction time. The reaction temperature and reaction time can be appropriately selected depending on factors such as the wavelength of the irradiated light.

In this way, the platinum-supported Mo oxide catalyst according to the embodiment of the present invention functions as a photocatalyst capable of converting light energy into chemical energy. Therefore, the carbon monoxide/methanol production method according to the embodiment of the present invention enables efficient production of methanol and carbon monoxide using light.

The present invention will be described in more detail below based on examples and comparative examples. However, the present invention is not limited to the following examples.

In Production Examples 1 to 7, platinum-supported Mo oxide catalysts were prepared, in Production Examples 8 to 13, platinum-supported catalysts using carriers other than molybdenum trioxide were prepared, and in Production Examples 14 to 15, molybdenum trioxide catalysts using carrier metals other than platinum were prepared.

[Production Example 1]
<Preparation of Pt/ _MoO3 >
1.25 g of hexaammonium heptamolybdate (AHM) (manufactured by Wako Pure Chemical Industries, Ltd.) was calcined at 450° C. for 4 hours in an air atmosphere to prepare molybdenum trioxide (MoO ₃ ).
_1.0 g of the obtained MoO3 was dispersed in 100 g of water, and 4.5 mL of an aqueous solution (35 mmol/L) of potassium tetrachloroplatinate ( _II ) ( _K2PtCl4 ) (manufactured by Nacalai Tesque, Inc.) and 0.2 g of urea were added, followed by stirring for 6 hours at 95°C. After stirring was completed, the product was removed from the reaction solution by centrifugation, washed with water, and then vacuum dried to obtain approximately 0.8 _g of powdered Pt/MoO3. The mass of the Pt particles supported on _MoO3 was 1.8% of the mass of the Mo oxide.

[Production Example 2]
<Preparation of Pt/ _{HxMoO3 -y} (100)>
The Pt/MoO ₃ obtained in Production Example 1 was subjected to hydrogen reduction treatment at 100° C. for 0.5 hours under a hydrogen partial pressure of 101.3 kPa to prepare Pt/H _x MoO _3-y (100).

[Production Example 3]
<Preparation of Pt/ _{HxMoO3 -y} (200)>
Pt/H _x MoO _3-y (200) was prepared in the same manner as in Production Example 2, except that the hydrogen reduction treatment was carried out at 200°C.

[Production Example 4]
<Preparation of Pt/ _{HxMoO3 -y} (300)>
Pt/MoO ₃ (300) was prepared in the same manner as in Production Example 2, except that the hydrogen reduction treatment was carried out at 300°C.

[Production Example 5]
<Preparation of Pt/ _{HxMoO3 -y} (400)>
Pt/MoO ₃ (400) was prepared in the same manner as in Production Example 2, except that the hydrogen reduction treatment was carried out at 400°C.

[Production Example 6]
<Preparation of _Pt6Cu / _{HxMoO3 -y} (300)>
1.0 _g of MoO3 obtained in Production Example 1 was dispersed in 100 g of water, and 1.6 mL of an aqueous solution (15.4 mmol/L) of copper (II) nitrate trihydrate (manufactured by Nacalai Tesque, Inc.), which is a copper precursor, and 0.2 g of urea were added, followed by stirring for 6 hours at 95° C. After stirring was completed, the product was removed from the reaction solution by centrifugation, washed with water, and then vacuum dried to prepare approximately 0.9 _g of powdered Cu/MoO3.

1.0 g of the obtained Cu/MoO ₃ was dispersed in 100 g of water, and 4.5 mL of an aqueous solution (35 mmol/L) of potassium tetrachloroplatinate (II) (K ₂ PtCl ₄ ) (manufactured by Nacalai Tesque, Inc.) and 0.2 g of urea were added, followed by stirring for 6 hours at 95° C. The molar ratio of Pt to Cu was Pt:Cu=6:1. After stirring was completed, the product was taken out of the reaction solution by centrifugation, washed with water, and then vacuum dried to obtain approximately 0.8 g of powdered Pt ₆ Cu/MoO ₃ .
Next, Pt ₆ Cu/MoO ₃ was subjected to hydrogen reduction treatment in the same manner as in Production Example 4 to prepare Pt ₆ Cu/H _x MoO _3-y (300) having oxygen defects introduced therein.

[Production Example 7]
< _Preparation of Pt/ _{W0.05Mo0.95Oz} ( ₃₀₀ )>
1.0 g of hexaammonium heptamolybdate (AHM) (manufactured by Wako Pure Chemical Industries, Ltd.) and 78 mg of ammonium paratungstate (manufactured by Wako Pure Chemical Industries, Ltd.), a tungsten precursor, were mixed in a mortar and then fired at ₄₅₀ ° C. for 4 hours in an air atmosphere to prepare approximately 1.0 g _{of W0.05Mo0.95Oz} .

1.0 _{g of the obtained W0.05Mo0.95Oz was dispersed} in 100 g of water, and 4.5 mL of an aqueous solution (35 mmol/L) of potassium tetrachloroplatinate ( _II ) ( _K2PtCl4 ) (manufactured by Nacalai Tesque, Inc.) and 0.2 g of urea were added, followed by stirring at 95°C for 6 hours. The molar ratio of W to Mo was W: _Mo = 5:95. After stirring was completed, the product was taken out of the reaction solution by centrifugation, washed with water, and then vacuum dried to obtain about 0.8 _g of powdered Pt/ _{W0.05Mo0.95Oz} .
Next, Pt/W _0.05 Mo _0.95 O _z was subjected to hydrogen reduction treatment in the same manner as in Production Example 4 to prepare Pt/W _0.05 Mo _0.95 O _z (300) having oxygen defects introduced therein.

[Production Example 8]
<Preparation of Pt/ _WO3 , Pt/ _WO3 (200), and Pt/ _WO3 (300)>
About 1.0 g of Pt/WO3 was obtained in the same manner as in Production Example ₁ , except that tungsten trioxide ( _WO3 ) (manufactured by Kojundo Chemical Laboratory Co., Ltd.), which absorbs visible light, was used as the catalyst support instead of _MoO3 .
Next, the obtained Pt/WO ₃ was subjected to hydrogen reduction treatment in the same manner as in Production Examples 3 and 4 to prepare Pt/WO ₃ (200) and Pt/WO ₃ (300).

[Production Example 9]
<Preparation of Pt/ _TiO2 , Pt/ _TiO2 (200), and Pt/ _TiO2 (300)>
About 1.0 _g of Pt/TiO2 was obtained in the same manner as in Production Example 1, except that titanium dioxide ( _TiO2 ) (P25, manufactured by Nippon Aerosil Co., Ltd.), which absorbs visible light, was used as the catalyst support _instead of MoO3.
Next, the obtained Pt/TiO ₂ was subjected to hydrogen reduction treatment in the same manner as in Production Examples 3 and 4 to prepare Pt/TiO ₂ (200) and Pt/TiO ₂ (300).

[Production Example 10]
<Preparation of Pt/ _SiO2 , Pt/ _SiO2 (200), and Pt/ _SiO2 (300)>
About 1.0 _{g of} Pt/SiO2 was obtained in the same manner as in Production Example 1, except that amorphous silica (fumed silica, manufactured by Aldrich Co.) was used as the catalyst support instead of _MoO3 .
Next, in the same manner as in Production Examples 3 and 4, the obtained Pt/SiO ₂ was subjected to hydrogen reduction treatment to prepare Pt/SiO ₂ (200) and Pt/SiO ₂ (300).

[Production Example 11]
<Preparation of Pt/V ₂ O ₅ (200) and Pt/V ₂ O ₅ (300)>
About 1.0 g of Pt/V ₂ O ₅ was obtained in the same manner as in Production Example 1, except that vanadium pentoxide catalyst (V ₂ O ₅ ) was used as the catalyst support instead of MoO ₃ .
Next, the obtained Pt/V ₂ O ₅ was subjected to hydrogen reduction treatment in the same manner as in Production Examples 3 and 4 to prepare Pt/V ₂ O ₅ (200) and Pt/V ₂ O ₅ (300).

[Production Example 12]
<Preparation of Pt/γ-Al ₂ O ₃ and Pt/γ-Al ₂ O ₃ (300)>
About 1.0 g of Pt/γ-Al ₂ O 3 was obtained in the same manner as in Production Example ₁ , except that aluminum oxide (γ-Al ₂ O ₃ ) (JRC-ALO-4, Catalysis Society reference catalyst) was used instead of MoO ₃ as the catalyst support.
Next, in the same manner as in Production Example 4, the obtained Pt/γ-Al ₂ O ₃ was subjected to hydrogen reduction treatment to prepare Pt/γ-Al ₂ O ₃ (300).

[Production Example 13]
<Preparation of Pt/ _ZrO2 (300)>
About 1.0 g of Pt/ZrO ₂ was obtained in the same manner as in Production Example ₁ , except that zirconium oxide (ZrO ₂ ) (RC-100, manufactured by Daiichi Kigenso Kagaku Kogyo Co., Ltd.) was used as the catalyst support instead of MoO 3.
Next, the obtained Pt/ZrO ₂ was subjected to hydrogen reduction treatment in the same manner as in Production Example 4 to prepare Pt/ZrO ₂ (300).

[Production Example 14]
<Preparation of Pd/ _{HxMoO3 -y} (200) and Pd/ _{HxMoO3 -y} (300)>
About 0.8 g of Pd/MoO ₃ was obtained in the same manner as in Production Example 1, except that sodium tetrachloropalladate (II) (Na ₂ PdCl ₄ ) (manufactured by Nacalai Tesque, Inc.) was used as the metal precursor instead of _{K 2} PtCl 4 .
Next, the obtained Pd/MoO3 was subjected to hydrogen reduction treatment in the same manner as in Production Examples 3 and ₄ to prepare Pd/ _{HxMoO3 -y} (200) and Pd/ _{HxMoO3 -y} (300) having oxygen defects introduced therein.

[Production Example 15]
<Preparation of Cu/ _MoO3 (200) and Cu/ _MoO3 (300)>
The Cu/MoO ₃ obtained in Production Example 6 was subjected to hydrogen reduction treatment in the same manner as in Production Examples 3 and 4 to prepare Cu/MoO ₃ (200) and Cu/MoO ₃ (300).

[Production Example 16]
<Preparation of _MoO3 (300)>
The MoO ₃ obtained in Production Example 1 was subjected to hydrogen reduction treatment in the same manner as in Production Example 4 to prepare MoO ₃ (300).

The structure and catalytic activity of the catalysts prepared in the manufacturing examples were evaluated as follows:

(1) UV-Vis-NIR
The UV-Vis-NIR absorption spectra were measured for the catalysts prepared in Production Examples 1 to 4. The measurements were performed using a UV-2600 (manufactured by Shimadzu Corporation) connected to an integrating sphere attachment ISR-2200 (manufactured by Shimadzu Corporation). Barium sulfate (BaSO ₄ ) powder was used as a reference sample. The measurement results are shown in FIG.

Pt/MoO ₃ (unreduced) showed almost no light absorption. On the other hand, Pt/H _x MoO _3-y (100), Pt/H _x MoO _3-y (200) and Pt/H x MoO _3-y (300) which had been subjected to hydrogen reduction treatment showed light absorption in a wide range from the visible light region to the infrared light region. In particular, Pt/H _x MoO _3-y (100) and Pt/H _x MoO _3-y (200) which had been subjected to hydrogen reduction treatment at 100°C and 200°C showed a wide range of light absorption with a maximum absorption wavelength around 590 nm. This is thought to be due to the induction _of surface plasmon resonance by light irradiation.

(2) _H2 -TPR
H ₂ -TPR measurements were carried out on the catalysts prepared in Production Examples 1, 8, 9, 10 and 12 that had not been subjected to hydrogen reduction treatment. The measurements were carried out using a BELCAT II (manufactured by Microtrack Bell Co., Ltd.) at a temperature rise rate of 5° C./min while flowing H ₂ diluted with Ar to a concentration of 5% by volume at 30 mL/min. Hydrogen consumption was detected by a thermal conductivity detector (TCD). The measurement results are shown in FIG. 2.

In Fig. 2, the vertical axis indicates the intensity of the signal detected by TCD. Although a small amount of hydrogen was observed to be absorbed in all catalysts, it was found that a large amount of hydrogen was absorbed in Pt/ _MoO3 using _MoO3 as a carrier at around 136°C. It was revealed that _MoO3 was reduced by hydrogen at around 136°C.

(3) XRD
The catalysts prepared in Production Examples 1 to 5 were measured by XRD. The measurement was performed using an Ultima IV (manufactured by Rigaku Corporation) at an acceleration voltage of 40 kV and a discharge current of 40 mV. Figure 3 shows the XRD patterns of the obtained catalysts.

Pt/ _MoO3 (unreduced) and Pt/ _{HxMoO3 -y} (100) showed structures close to the orthorhombic crystal of _MoO3 . On the other hand, Pt/ _{HxMoO3 -y} (200) and Pt/HxMoO3 _{-y (300) which were subjected to hydrogen reduction treatment at 200°C and 300°C showed almost no peaks derived from MoO3, and were found to be amorphous. Pt/HxMoO3-y ( 400 )} obtained by hydrogen reduction treatment at 400 _° C had a structure closer to the monoclinic crystal of _MoO2 than Pt/ _{HxMoO3 -y} (300). From the above results, it was confirmed that the structure of the platinum-supported Mo oxide catalyst changes depending on the hydrogen reduction treatment temperature.

(4) T.G.
The hydrogen doping amount (x) and the amount of oxygen vacancies (y) were determined by TG for the catalysts prepared in Production Examples 1 to 5. The measurements were performed using Thermo plus EVOII (manufactured by Rigaku Corporation) in a nitrogen flow of 50 mL/min or in air flow at a temperature increase rate of 10° C./min.

Pt/ _MoO3 (unreduced) x = 0, y = 0; Pt _/ HxMoO3 _-y (100) x = 1.91, y = 0.02; Pt/HxMoO3 _{- y} (200) x = 1.15, y = 0.28; Pt/HxMoO3 _{- y} (300) x = 0.35, y = 0.74; Pt/ _{HxMoO3 -y} (400) x = 0.02, y = 1.04. It was found that the hydrogen doping amount (x) tends to decrease and the oxygen vacancy amount (y) tends to increase with increasing hydrogen reduction temperature.

(5) XPS
The catalysts prepared in Production Examples 1 to 4 were measured by XPS. The measurement was performed using an ESCA-3400 (manufactured by Shimadzu Corporation) as the apparatus and MgK _α rays (1253.6 eV) as the radiation source. The results are shown in FIG.

Only Mo ⁶⁺ was present in Pt/MoO ₃ (untreated) before hydrogen reduction treatment, but Mo 5+ and Mo ⁴⁺ were present in Pt/H _x MoO _3-y (100), Pt/H _x MoO _3-y (200) and Pt/H _x MoO _3-y (300) after hydrogen reduction treatment in addition to Mo ⁶⁺ . This confirmed that oxygen defects were introduced into Pt/MoO ₃ by hydrogen reduction treatment. In addition, since the ratio of ^{Mo 4+ increased} as the hydrogen reduction treatment temperature increased, it was also confirmed that the amount of oxygen defects introduced increased as the hydrogen reduction temperature increased.

(6) TEM
The Pt/H _x MoO _3-y (200) prepared in Production Example 3 was observed by TEM. The TEM was H-800 (manufactured by Hitachi, Ltd.), and the measurement was performed at an accelerating voltage of 200 kV. The photograph taken is shown in Figure 5. It was confirmed that Pt particles with an average particle size of 2.4 nm were highly dispersed and fixed on the Mo oxide.

Using the catalyst prepared in Production Example, a deoxygenation reaction of carbon dioxide was carried out.
[Example 1]
A carbon dioxide deoxygenation reaction was carried out using the catalysts prepared in Production Example 4 and Production Examples 8 to 16 that had been subjected to hydrogen reduction treatment at 300°C. 50 mg of the catalyst and 15 mL of 1,4-dioxane as a solvent were placed in a stainless steel pressure-resistant reaction vessel, and after introducing carbon dioxide gas and hydrogen gas, the reaction was carried out in a dark place at 200°C for 20 hours. The partial pressure of carbon dioxide was 1 MPa, and the partial pressure of hydrogen was 3 MPa.
After the reaction was completed, the products were analyzed using a gas chromatograph with a methanizer and a flame ionization detector (GC-FID). The conversion rate (%) of carbon dioxide, the selectivity of the produced methanol, carbon monoxide and methane, and the catalyst turnover number (TON) for all products based on the amount of supported metal, which were obtained from the analysis results, are shown in Table 1.

When _MoO3 was used alone, the deoxygenation reaction of carbon dioxide hardly proceeded. On the other hand, when Pt/ _{HxMoO3 -y} (300) prepared in Production Example 4 was used, a specifically high carbon dioxide conversion rate and methanol selectivity were obtained compared to the cases where a catalyst in which Pt was supported on a carrier other than _MoO3 and a catalyst in which a metal other than Pt was supported on _MoO3 were used.

[Example 2]
Using the Pt/ _{HxMoO3 -y} (300) prepared in Production Example 4 as a catalyst, a carbon dioxide deoxygenation reaction was carried out in the same manner as in Example 1. The reaction time was set to 120 hours, and the time-dependent changes in the yield and selectivity of the product were analyzed. The results are shown in Figures 6 and 7.

Figures 6 and 7 show that the amount and selectivity of carbon monoxide produced, which were high at the beginning of the reaction, decreased as the reaction time increased, while the amount and selectivity of methanol produced increased.

[Example 3]
Using Pt/H _x MoO _3-y (300) prepared in Production Example 4 as a catalyst, a reaction was carried out under the conditions shown in Table 2, and the mechanism by which carbon monoxide and methanol are produced from carbon dioxide was analyzed.

Unlike the reaction system with a carbon dioxide partial pressure of 1.0 MPa and a hydrogen partial pressure of 3.0 MPa, under low-pressure conditions with no hydrogen being introduced and a carbon dioxide partial pressure of 1.0 MPa, the carbon dioxide conversion rate was low, and only carbon monoxide was produced, with no methanol. On the other hand, in a system without carbon dioxide introduction and with a carbon monoxide partial pressure of 0.1 MPa and a hydrogen partial pressure of 3.0 MPa, the conversion rate and methanol selectivity were high. From these results, it is presumed that in the carbon dioxide deoxygenation reaction using a platinum-supported Mo oxide catalyst, methanol is produced via carbon monoxide. It is also believed that the reaction of producing methanol from carbon monoxide proceeds more easily under high-pressure conditions.

[Example 4]
Using the catalysts prepared in Production Examples 1 to 5, a carbon dioxide deoxygenation reaction was carried out in the same manner as in Example 1. The results of determining the carbon dioxide conversion rate and the product selectivity are shown in Figure 8. Also, the correlation between the hydrogen reduction temperature of the catalyst, the product yield, the hydrogen doping amount (x) and the amount of oxygen vacancies (y) of each catalyst determined above is shown in Figure 9.

8 and 9, it was found that the amount of oxygen defects increases as the hydrogen reduction treatment increases, and the yield of methanol increases accordingly. Pt/ _{HxMoO3 -y} (200) and _Pt /HxMoO3 _-y (300) showed particularly high catalytic activity, and the use of these catalysts also increased the selectivity of methanol.

On the other hand, it was revealed that the catalytic activity of Pt/ _{HxMoO3 -y} (400) which was subjected to hydrogen reduction treatment at 400°C was reduced compared to Pt/ _{HxMoO3 -y} (300). Since the structure of Pt/ _{HxMoO3 -y} (400) is closer to the monoclinic crystal structure of _MoO2 compared to Pt/ _{HxMoO3 -y} (300) which has an amorphous structure, it is believed that the change in structure is the cause of the reduction in catalytic activity.

[Example 5]
Using the catalysts of Production Examples 4, 6 and 7, a carbon dioxide deoxygenation reaction was carried out in the same manner as in Example 1.

The platinum-supported Mo oxide catalyst, even if it is Pt ₆ Cu/MoO ₃ (300) in which the Pt particles contain metal elements other than Pt, or Pt/W _0.05 Mo _0.95 O _z (300) in which the Mo oxide carrier contains metal elements other than Mo, showed high activity in the deoxygenation reaction of carbon dioxide, similar to Pt/H _x MoO _{3-y (} 300). In addition, when Pt ₆ Cu/MoO ₃ (300) was used, the amount of carbon monoxide produced increased by about 1.2 times compared to when Pt/H _x MoO 3-y (300) was used. When Pt/W _0.05 Mo _0.95 O _z (300) was used, the amount of methanol produced increased by about 1.2 times compared to when Pt/H _x MoO _3-y (300) was used.

[Example 6]
A carbon dioxide deoxidation reaction was carried out using Pt/H _x MoO _3-y (200) prepared in Production Example 3. 100 mg of the catalyst was placed in a quartz reactor, and after introducing carbon dioxide gas and hydrogen gas, the reaction was carried out at 140° C. for 2 hours in the dark and under irradiation of visible light (>450 nm). The partial pressure of carbon dioxide was 0.5 atm, and the partial pressure of hydrogen was 0.5 atm. A xenon lamp was used as the visible light irradiation device. The change over time in the amount of carbon monoxide produced (mmol) per 1 g of catalyst is shown in FIG. 10.

It was confirmed that the amount of carbon monoxide produced was approximately twice as much under visible light irradiation as in the reaction in the dark. It is believed that Pt/ _{HxMoO3 -y} (200) reduced with hydrogen at 200°C exhibited strong light absorption due to surface plasmon resonance under visible light irradiation, and that this improved catalytic activity.

[Example 7]
Using the catalysts prepared in Production Examples 3, 8 to 10, and 14 to 15 and subjected to hydrogen reduction treatment at 200° C., a carbon dioxide deoxygenation reaction was carried out under visible light irradiation in the same manner as in Example 6. The change over time in the amount of carbon monoxide produced (mmol) per gram of catalyst is shown in FIGS.

11 and 12, it was confirmed that a platinum-supported Mo oxide catalyst, which has _MoO3 as a carrier and Pt supported thereon, becomes a catalyst having high activity under light irradiation by being subjected to hydrogen reduction treatment.

[Example 8]
Using the catalysts prepared in Production Examples 2 to 4, a carbon dioxide deoxygenation reaction was carried out under visible light irradiation in the same manner as in Example 6. The change over time in the amount of carbon monoxide produced (mmol) per gram of catalyst is shown in Figure 13. Furthermore, the correlation between the hydrogen reduction temperature, the amount of carbon monoxide produced (mmol), the amount of hydrogen doped (x) and the amount of oxygen vacancies (y) of each catalyst is shown in Figure 14.

It was revealed that the platinum-supported Mo oxide catalyst exhibited the highest activity under light irradiation when hydrogen reduction treatment was performed at 200°C.

[Example 9]
A carbon dioxide deoxidation reaction was carried out in the same manner as in Example 6, except that Pt/H _x MoO _3-y (200) prepared in Production Example 3 was used as a catalyst, and light-emitting diode (LED) lamps (green, red, blue) were used instead of a xenon lamp as an irradiation device. The change over time in the amount of carbon monoxide produced (mmol) per 1 g of catalyst is shown in FIG. 15. In addition, the UV-Vis-NIR absorption spectrum of Pt/H _x MoO _3-y (200), the wavelength of each LED, and the increase rate of the amount of carbon monoxide produced when irradiated with each LED are shown in FIG. 16. The increase rate of the amount produced is a value obtained by comparing with the amount produced during the reaction in a dark place.

The amount of carbon monoxide generated was highest when the irradiated light was LED (green), followed by LED (red) and then LED (blue). This coincides with the order of highest absorbance at _each wavelength of LED (green), LED (red) and LED (blue) in the UV-Vis-NIR absorption spectrum of Pt/H _x MoO 3-y (200), as confirmed in Fig. 16.

The carbon monoxide/methanol production method of the present invention can be used for the efficient conversion of carbon dioxide, a substance that causes global warming, into basic chemical products.

Claims (10)

Mo oxide including molybdenum trioxide;
and platinum particles supported on the Mo oxide,
The molybdenum trioxide has oxygen vacancies,
When the Mo oxide is represented by the general formula: H _x MoO _3-y ,
0<x<2.0, and
0.2≦y≦0.8 is satisfied,
A platinum-supported Mo oxide catalyst that does not contain titanium oxide and promotes a reaction for producing at least one of carbon monoxide and methanol by reduction of carbon dioxide. The platinum-supported Mo oxide catalyst according to claim 1, wherein the Mo oxide has an amorphous structure. 3. The platinum-supported Mo oxide catalyst according to claim 1 , wherein surface plasmon resonance of the Mo oxide is induced under irradiation with visible light. 4. The platinum-supported Mo oxide catalyst according to claim 1 , wherein the mass of the platinum particles supported on the Mo oxide is 0.1% or more and 5% or less of the mass of the Mo oxide. The platinum-supported Mo oxide catalyst according to any one of claims 1 to 4 , wherein the platinum particles contain a metal element M1 other than platinum. The platinum-supported Mo oxide catalyst according to any one of claims 1 to 5 , wherein the Mo oxide contains a metal element M2 other than molybdenum. A method for producing carbon monoxide/methanol, comprising a step of carrying out a deoxygenation reaction of carbon dioxide in the presence of the platinum-supported Mo oxide catalyst according to claim 1 and hydrogen to produce at least one of carbon monoxide and methanol. The method for producing carbon monoxide/methanol according to claim 7 , wherein the deoxygenation reaction is carried out in an atmosphere of 300° C. or less. The method for producing carbon monoxide/methanol according to claim 7 or 8, wherein the deoxygenation reaction is carried out under irradiation with visible light that induces surface plasmon resonance of the Mo oxide. The method for producing carbon monoxide/methanol according to claim 9 , wherein the deoxygenation reaction is carried out in an atmosphere of 150° C. or less.

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